Pitfalls to adding cellulose in unvented attic?
I'm helping a homeowner improve his 1974 ranch, zone 5 Ohio. Attic currently has 6" of cellulose, no air sealing. Blower door results were predictably awful. After removing all recessed light fixtures and fully air sealing the attic floor, I'll be adding more cellulose. There are no mechanicals in the attic, except for a plumbing vent and a little wiring.
Question: are there any potential problems in simply blowing in more cellulose? Even up to touching the roof sheathing near the eaves? (It wouldn't take much, in fact, to completely fill the attic, if one was inclined..)
Issue: there is essentially no venting of the attic space. I understand that this is not necessarily a problem--there is no evidence of moisture damage anywhere on the roof deck or the ceiling below, so neither vapor nor ice damming seem to have been an issue in the roof's first 40 years.
The roof is low-pitch (only 4:12) and constructed with 2x6 rafters, which extend past the wall for a nice 4' overhang. There is no gable or soffit venting, and fiberglass batts are stuffed in the 5.5" space above the wall plate to keep loose fill out of the overhang. (With no venting, there is no wind washing.) Ridge venting was cut in with the most recent asphalt roof, just that nominal stuff that looks as ineffective as it is. My worry is that perhaps the space HAS been vented, via the ceiling air leaks and the ridge venting, and that air sealing and extra fill will change the thermodynamics completely.
Any analysis and wisdom would be appreciated!
Posted Aug 20, 2014 9:17 AM ET
Edited Aug 20, 2014 9:50 AM ET
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